Rayon and method of manufacturing same



Patented Feb. 23, 1943 RAYON AND METHgD OF MANUFACTURING Isaac P. Davis, Swarthmore, Pa., assignor to American Viscose Corporation, Wilmington,

Del., a corporation of Delaware v No Drawing. Application December 10, 1941,

' Serial N0. 422;61

8 Claims. (CI. 18-64) In the first place the tensile strength was not suiliciently high to enable it to compete with the customary cotton cords. In the second place, the ultimate elongation oi the rayon was so reat that tires constructed from cords made of this rayon would swell or grow during their lifetime by about 01' their original size.

Thus it was proposed by Suter in British Pat ent 343,617 that the type of rayon known as Lilienfeld yarn, characterized by very high tenacity and a very low ultimate elongation, should be used for this purpose. This has been tried and although it is more successful than the ordinaryrayon, it still does not give results in-proportion to the tenacity of the cord so manufactured. It thus appears that there is still a third property for the production of the reinforcing cords which neither of, the rayons so far tried appears to possess. This property as Naso.

distinguished from tenacity we will call toughness or resistance to shear.

I have produced a special yarn by projecting viscose into a coagulating bath containing zinc sulphate in proportions and under conditions hereinafter described, which special yarn is characterized by unusual toughness. The ultimate elongation exceeds 20%, which is much too high for the production of reinforcing cords, as it has been found that best results. are obtained when the ultimate elongation is between 9 and 14%. At present no yarn can be spun direct with this low extensibility without sacrificing the toughness. A test for toughness is made .on a cord flexing machine similar to that referred to in U. 8. Patent 1,632,201. Thus it would seem that the high extensibility of this particular type of yarn is necessary to its toughness. although rendering it unsuitable for use in tire cords.

Ordinary cotton yarn will stand about three thousand cycles of flexing on such a machine,

the special tough, zinc sulphate bath coagulated yarn will stand about thirty thousand cycles,

whereas the special tough, zinc sulphate bath coagulated yarn with the special treatment hereinafter described will stand about thirty-six thousand cycles.

It is characteristic oi the coagulating bath that it contains zinc sulphate in certain specific quantitles, and it is characteristic of the process that the special yarn can be given an abnormally high stretch while spinning.

, The dehydration and neutralization which take place in producing the filament oi regenerated cellulose result in an extremely dry and quite plastic yarn, but owing to the toughness oi the freshly spun thread there is a limit to the amount of stretch that can be given the yarn. A well known procedure to apply a stretch to the freshly spun thread is by carrying it over two successive revolving wheels. the second of which has a peripheral speed greater than theiirst by to I give below the preferred composition of the spinning or coagulating bath and also'the limits which can be used and still get the desired result. The specific gravity data are given at 40 Preferred Although the aboveprocess is applicable to the usual type of viscose spinning solution or dope, employing wood pulp as a base, threads of considerably higher tenacity and toughness are produced it cotton pulp is substituted in part or in whole for the wood pulp. Similar advantage is obtained it a wood pulp which has been purifled to a high alpha-cellulose content is used. The cellulose content of the viscose solution may conform to the usual figure of about 7%. and the sodium hydroxide concentration maybe approximately that of the cellulose, or even higher, suchas8t or 9%.

Yarn made from such a cotton viscose solution or dope, spun in the above-mentioned high zinc sulphate bath, can be given a stretch in the spinning in excess of 40%preferably The result is that the tensile strength of the yarn is increased considerably without detracting from the yarn's toughness and elasticity. Thus, uch a stretched yarn has a dry strength of about 3 grams per denier with an extensibility of from to The wet strength is about 1 /2 grams per denier. If a stretch were tried with the normal viscose and normal bath the dry tenacity would be much less than 3 grams per denier, and the extensibility would be too low to be practical.

If during the process of app yin stretch to the thread thus produced. heatis applied to the thread either by means of direct steam or by immersing it in hotwater ing point, th amount of the stretch can be in-- creased to as much as 100%. Such increase stretch is maintained, that the ultimate elongation can be reduced to the above named figure of from 9%to 14% without any decrease in the toughness property of this yarn.

Furthermore, there is not only an increase in tenacity' as measured in grams'per denier, but

substantially at the boilfrom the 50% previously described produces 1 threads having a much higher tenacity than heretofore, without excessive reduction in exten stretching process to the the spinning bath Drevithe plasticizing medium during the stretching I operatiornas the water'removes the excess bath before tendering or crystallization can take place.

It has been found that the best results are ob-- tained when the thread is subjected to the action of water at or near the boiling point over a distance of about 18" between two successive godet wheels, the second of a peripheral speed substantially 80% than that of the first. If the water thus used is recirculated, appreciable amounts of precipitating bath constituents will be accumulated therein, and according to the amount oi. fresh water added, may approach the concentrations present in the precipitating bath as a limit.

The following are the limits of operation for an actual increase in breaking load of the thread itself. An illustration of the effect of afterstraining is shown in the appended table.

Beiore Alter stretching stretching Denier": 306 281 Breaking load, grams 873 006 Tenacity, grams per denier 2. 86 3. 21 Ultimate extensibility 18. 0 9. I

-' Such a result could not have been anticipated from the prior knowledge, and is an inherent which is revolving at greater both the spinning bath and, the plastlcizing agent used in stretching, also the preferred conditions.

The specific gravity data are given at 40 C. and the composition data as per cent by,weight.

Yarn spun into the above preferred bath from viscose made of 100% cotton pulp hereinbefore described and given a stretch of 80% while subjected to the action of water at a temperature of 100 C. will have a dry strength in excess of 3 grams per denier, a dry extensibility of 20% and a wet strength of 2 /2 grams per denier.

' It has been known that if rayon yarns as ordinarily manufactured are subjected to strain while wet, and dried while such strain is maintained, the denier and extensibility are reduced, and the tenacity, as expressed in grams per denier, is increased in proportion to the decrease in denier, the actual breakingload remaining the same, or being slightly reduced. This, however, is done at a considerable sacrifice in toughness.

I have now discovered that if this special tough, zinc sulphate bath coagulated yarn is stretched while wet by an amount equal to from 6% to 15% of its length, and dried while this characteristic of the yarn made according to the aforesaid copending application.

It must be understood that the stretching action above disclosed is carried out on a fully regenerated cellulose thread, from which all precipitating bath acid has been removed. It must not be confused with the stretch of from 40 to 100% which is applied to the partially regen-. erated thread in the acid condition. The special stretch or after-straining may be applied to wet yarn which has passed through the steps of precipitating, stretching with or without application of heat, and deacidifying, or to dry yarn which has been dried following deacidiflcation as above, and rewet preceding stretching. The operations of desulphurizing and bleaching may be added in either case, but are not essential for the operation of the process.

The stretching operation may be carried out in any known manner by which a thread may be stretched. It may be subjected to a frictional tension of suillcient magnitude to produce the desired increase in length and then while this tension is maintained, be wound on a drum and subsequently subjected to the action of heat.

Likewise, it may be subjected to a frictional tension and'whlle maintained under this tension passed over heated rollers whereby it is dried while still extended and then wound on a suitable collection device. Or it may be fed on to a drum bymeans of a measuring wheel or roller running at a speed from 6 to 15% slower than the drum on which the thread is being collected and the thread on the'drum subsequently sub- ,iected to the action of heat to dry it. Or itmay be continuously fed from a set of nip rollers on to a set of heated drums from which it is removed by a suitable yarn collecting device, the

set of rollers revolving at a speed from 6 to 15% slower than the heated drums.

The same effect may be obtained without a deliberate act of stretching in the following man-" her. When the rayon yarn coagulated in the zinc sulphate bath is removed from the precipitating bath it is subjected to a stretch of from 40 to During subsequent finishing operations, such as deacidifying and desulphurizing there is a tendency for this yarn to shrink back from 10 to 25% of its length according to the amount of stretch it has been given. If this tendency to shrink is opposed, either in whole or in part, while these operations are being carried out and the yarn dried while the shrinking tendency is still being opposed, an effect will be obtained identical with that described above wherein the yarn is first allowed to shrink and has been subsequently stretched back to the desired point.

It is true that if this yarn is subjected to the action ofwater and permitted to shrink freely, it will regain a major portion of its former ultimate elongation. Nevertheless, the straining action is permanent even in moderately high humidities as long as no water is allowed to touch the yarn. This is no disadvantage in the preparation of tire cords inasmuch as water does not touch the yarn at all or else not until after the cord has been manufactured. In this condition the internal strains of the cord twist are such as to oppose the shrinkage and leave the yarn substantially in its original form. This last is more particularly true when the cords are treated in the form of a warp by impregnating with rubber latex, an operation which precedes incorporation in the tire body.

I claim:

1. In the process of manufacturing rayon yarn, characterized by high tensile strength, toughness and elasticity, the steps of projecting viscose spinning solution into a coagulating bath containing from 6.5% to 9.0% sulphuric acid, from 14% to 18% sodium sulphate, and from 4% to 8% zinc sulphate, subjecting the yarn to a Spinning stretch of 25% to 50%, processing the yarn, subjecting said processed yarn while wet to a stretch of from 6% to 15%, and drying the yarn while this stretch is maintained.

2. In the process of manufacturing rayon yarn, characterized by high tensile strength, toughness and elasticity, the steps of projecting viscose spinning solution into a coagulating bath containing by weight from 6.5% to 12% sulphuric acid, from 14% to 26% sodium sulphate, and from 4% to 10% zinc sulphate, removing the yarn from the bath and subjecting it in an aqueous heating fluid at a temperature of from 60 C. to 100 C. to a stretch of from 40 to 100%, opposing shrinkage of the stretched yarn during subsequent processing operations, and drying the yarn while this stretch is maintained.

3. In the process of manufacturing rayon yarn having improved tensile strength, toughness and elasticity, by projecting viscose spinning solution into an aqueous coagulating bath containing by weight from 6.5% to 12% sulphuric acid,

from 14% to 26% sodium sulphate, and from 4% to 10% zinc sulphate and stretching the freshly spun yarn from 40% to 100% and processing the yarn without more than 25% shrinkage, the improvement which comprises reducing the ultimate elongation of said yarn tofrom 9% to 14% without any decrease in the toughness or in the tenacity by stretching the processed yarn while wet by an amount equal to from 6% to 15% of its length and drying the yarn while this stretch is maintained, thereafter subjecting said yarn to a waterproofing treatment, and preventing any water from touching said yarn after said drying step and before said waterproofing treatment.

4. An an article of manufacture, rayon yarn characterized by high tensile strength, toughness and elasticity and obtained by coagulating viscose spinning solution in a coagulating bath containing by weight from 6.5 to 9% sulphuric acid, from 14% to 18% sodium sulphate, and from 4% to 8% zinc sulphate, said yarn being subjected Search Room to a spinning stretch of to processed without increasing the shrinkage thereof and thereafter stretched from 6% to 15% of its length and dried while so stretched, said yarn consisting substantially of re enerated cellulose and having a dry tenacim grams per denier, and an ultimate elongation between 9% and 14%.

5. As an article of manufacture, rayon yarn characterized by high tensile strength, toughness and elasticity and obtained by coagulating viscose spinning solution in a coagulating bath containing by weight from 6.5 to 12% sulphuric acid, from 14% to 26% sodium sulphate, and from 4% to 10% zinc sulphate said freshly spun yarn being stretched from 40% to 100% while subjected to an aqueous heating fluid at a temperature of from C. to C., and thereafter without more than 25% shrinkage taking place stretched from 6% to 15% of its length and dried while so stretched, said yarn consisting substantially of regenerated cellulose and having a dry tenacity of at least three grams per denier and an ultimate elongation between 9% and 14%.

6. In the process of manufacturing viscose rayon yarn characterized by toughness and elasticity, the steps of projecting the viscose spinning solution into an acid coagulating bath containing by weight from 6.5% to 12% sulphuric acid, from 14% to 26% sodium sulfate and from 4% to 10% zinc sulphate, removing the yarn from said zinc sulphate bath and subjecting it in the acid condition to the action of an aqueous heating fluid at from 60 to 100 C. and simultaneously stretching it, deacidifying the stretched yarn, thereafter sulfate and zinc sulphate in high concentrations from 4% to 10%, removing the partially regenerated yarn from said high zinc sulphate bath and subjecting it in the acid condition to the action of an aqueous heating fluid at a temperature of from 60 to 100 C. and simultaneously stretching it, deacidifying the stretched yarn, thereafter again stretching the fully regenerated yarn while wet, and drying it while said after-stretch is maintained.

8. In the process of manufacturing viscose rayon yarn characterized by high tensile strength, toughness and elasticity, the steps of projecting the viscose spinning solution into a dilute acid coagulating bath containing by weight from 6.5% to 12% sulphuric acid, from 14% to 26% sodium sulfate and from 4% to 10% zinc sulphate, removing the partially regenerated yam from said high zinc bath and subjecting it in the acid condition to the action of an aqueous heating fluid at a temperature of from 60 centigrade to 100 centigrade and simultaneously stretching it from 40% to 100%, deacidifying the stretched yarn, thereafter again stretching the fully regenerated yarn from 6% to 15% while wet, and drying it while said after-stretch is maintained.

ISAAC P. DAVIS. 

